This invention relates to a circuit board testing apparatus and method for testing such electric state as continuity, open-circuit, short-circuit, of a number of wirings formed on a circuit board.
It should be appreciated that this invention is applicable to testing of electric state of wirings formed on any of a variety of circuit boards or substrates such as printed circuit boards, flexible circuit boards, multi-layer circuit boards, glass substrates for use in liquid crystal display or plasma display panels, and film carriers for use in semiconductor packages, and that the term xe2x80x9ccircuit boardsxe2x80x9d as used in this specification may be any of these variety of boards.
Circuit boards are formed with a wiring pattern by a number of wirings thereon. There have been proposed a number of testing apparatus to test whether the wiring pattern has been formed as designed. Recent trend of making small-sized and light-weighted electronic devices necessitates arranging a wiring pattern in a complex manner in a small area. Thus, it is difficult to test open-circuits and short-circuits of wirings by direct contact of probes with the circuit board. Therefore, there has been proposed a contactless testing apparatus to test electric state of a wiring pattern such as open circuit without causing direct contact of probes with a minute conductive pad.
For example, Japanese Patent No. 3080158 discloses this type of apparatus which is adapted for testing an open or short-circuit of a wiring formed on a circuit board. In the apparatus, specifically, an electromagnetic wave is irradiated onto a pad connected to each wiring of a circuit pattern formed on a circuit board to thereby cause discharge of electrons from the pad owing to photoelectric effect. The open or short-circuit of the wiring is tested based on an electric current which is caused by discharged electrons to run into a ground (GND) plane or external metallic plate capacitively coupled.
Japanese Unexamined Patent Publication No. 8-278342 discloses a printed board testing apparatus which detects electrons discharged in a space owing to photoelectric effect to test continuity or open-circuit of wirings of the printed board. Specifically, an electric charge sensor and an electromagnetic wave generator are movably provided above the printed board with a specified gap or distance therebetween. The electric charge sensor and the electromagnetic wave generator are relatively moved over the printed board to scan discharged electrons. The electric state of wirings are judged based on detected changes of the electric current.
The aforementioned conventional arts are suffered from the following drawbacks. In the conventional art, an electromagnetic wave is merely irradiated onto a pad or wirings. Electrons which are discharged owing to photoelectric effect upon irradiation are returned to the pad and wirings, or dispersed in the space without being utilized for the testing.
Further, discharged electrons form a spatial charge region, and lower the electron discharging efficiency of the photoelectric effect. Even if electrons are discharged instantaneously owing to photoelectric effect, accordingly, current flowing in the ground plate or external metallic plate cannot be measured with reliability. Thus, it is difficult to accomplish stable and precise test efficiency.
In the apparatus of Japanese Unexamined Patent Publication No. 8-278342, further, the electric charge sensor and the electromagnetic wave generator are moved relatively to the printed board to scan discharged electrons, which consequently increases the size of the apparatus. It will be seen that in the case of producing a vacuumed space between the printed board and the electric charge sensor and the electromagnetic wave generator, a larger-sized vacuuming unit is required.
It is an object of the present invention to provide a circuit board testing apparatus and testing method which are free from the problems residing in the prior art.
It is another object of the present invention to provide a circuit board testing apparatus and testing method which can judge the continuity and/or short-circuit of wirings formed on a circuit board accurately and stably.
It is still another object of the present invention to provide a circuit board testing apparatus and testing method which can assure more efficient testing of the continuity and/or short-circuit of wirings formed on a circuit board.
It is yet another object of the present invention to provide a circuit board testing apparatus which is small in size and enables test of wirings in a short time.
It is still further object of the invention to provide a circuit board testing apparatus and testing method that enables testing of wirings formed on the circuit board with the test signals being derived from the circuit board without mechanical mechanic contact at least on one side of the circuit board.
According to an aspect of the present invention, a circuit board testing apparatus is adapted for testing continuity and/or short-circuit of wirings formed on a circuit board. First terminals of the wirings are irradiated with an electromagnetic wave so that electrons are discharged from the first terminals by photoelectric effect. Discharged electrons are trapped by an electrode which is electrically biased to have a higher potential than that of the second terminals of the wirings, thereby causing an electric current to flow through the wirings via the electrode. Existence of an open-circuit and/or a short-circuit in the wirings is judged based on the current flowing the wirings.
According to an embodiment of the invention, the first terminals are irradiated with the electromagnetic wave alternatively, one at a time. Also, the second terminals of the wirings are supplied with voltage one at a time. Alternatively, a voltage may be supplied to the second terminal of a wiring adjacent to a selected wiring of which first terminal is irradiated by the electromagnetic wave.
For the testing of a circuit board having wirings including a pair of terminals formed on a surface of the circuit board and an electric conductor formed on the surface of the circuit board or inside the circuit board and connected to the pair of terminals, there may be preferably provided a second electrode to be capacitively coupled to the electric conductor. The continuity of the electric conductors is judged based on a current value when the first terminal of a target wiring is irradiated and another current value when the second terminal of the target wiring is irradiated.
For the testing of a circuit board including wirings having electric conductors formed on the surface or inside of the circuit board and electrically connected to respective first and second terminals, there may be preferably provided a second electrode to be capacitively coupled to the electric conductors. The short-circuit between wirings is judged based on a current value when the one of the first terminals is irradiated and another current value when another of the first terminals is irradiated.
Alternatively, the electromagnetic wave may be collectively irradiated onto the first terminals of the wirings. In this case, it may be preferable to provide a power source having a first pole connected to the electrode and a second pole connected to the second terminal of a wiring selected for the test. The second terminals of the wirings other than the target wiring may be connected to the first pole of the power source.
Alternatively, the second terminal of a target wiring may be connected to the second pole of the power source by way of a current detector for detecting a current of the target wiring while the second terminals of the wirings other than the target wiring are connected to the second pole of the power source bypassing the current detector.
It may be preferable to enclose the first terminals of the wirings within an airtight closed space, and depressurize the closed space. The degree of depressurization is preferably 10xe2x88x922 atm.
A circuit board testing apparatus or method according to the present invention provide accuracy and efficiency in the testing of the continuity and/or short-circuit of wirings on a circuit board because electrons discharged by photoelectric effect are captured by the electrically biased electrode and cause an enhanced electric current through the wirings connected with the electrode.
These and other objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments/examples with reference to the accompanying drawings.